(a) Field of the Invention
This invention relates to novel compounds classified in the field of organic chemistry as fluorans useful as color precursors, particularly in the area of carbonless duplicating, for example, pressure-sensitive and thermal-responsive marking systems; to pyridylethyl-substituted anilines and to (pyridylethylaminophenyl)carbonylbenzoic acids useful as intermediates in preparing them; to processes for preparing said fluorans; and to pressure-sensitive duplicating systems and thermal-responsive marking systems containing the same.
(b) Description of the Prior Art
Several classes of organic compounds of widely diverse structural types are known to be useful as colorless precursors for carbonless duplicating systems. Among the more important classes, there may be named phenothiazines, for example, benzoyl leuco methylene blue; phthalides, for example, crystal violet lactone; fluorans, with which this invention is concerned, for example, 2-anilino-6-diethylaminofluoran and 2-dibenzylamino-6-diethylaminofluoran; and various other types of colorless precursors currently employed in commercially accepted carbonless copy systems. Typical of the many such systems taught in the prior art are those described in U.S. Pat. Nos. 2,712,507, 2,800,457 and 3,041,289 which issued July 5, 1955, July 23, 1957 and June 26, 1962, respectively. Many of the color formers in the prior art suffer one or more disadvantages such as low tinctorial strength, poor light stability, low resistance to sublimation, low susceptibility to xerographic copiability of the color-developed form and low solubility in common organic solvents, the latter disadvantage requiring the use of specialized and expensive solvents in order to obtain microencapsulated solutions of sufficient concentration for use in pressure-sensitive copying systems.
The following item to date appears to constitute the most relevant prior art with regard to the instant invention.
U.S. Pat. No. 3,901,918, issued Aug. 26, 1978, discloses novel fluoran compounds such as 2-bis-(5',6',7',8'-tetrahydro-2'-naphthylmethyl)amino-6-diethylaminofluora n and 2-(2'-thenylamino)-8-dimethylbenz[c]fluoran, which are useful as a coloring material for record material systems, such as pressure-sensitive copying paper or heat-sensitive copying paper, wherein colored images are formed by an electron-donor-acceptor color-forming reaction between coloring material and acidic material. This reference teaches, in pertinent part, the species 2-(N-2'-pyridylmethyl-N-acetylamino)-6-dimethylamino-3'-4'-5'-6'-tetrachlo rofluoran.